Present invention relates to a process for the recovery of substantially anhydrous carboxylic acids from gaseous mixtures containing such carboxylic acids and water, and is particularly applicable to the C.sub.2 -C.sub.5 monocarboxylic acids. Other compounds may also be present in the gaseous mixture.
In various industrial processes there results a high temperature gaseous mixture containing carboxylic acids and water, and sometimes various other compounds such as inert gases. Usually these gaseous mixtures are obtained in vapor phase oxidation processes where hydrocarbons, carbonyl compounds or alcohols or mixtures of such, are oxidized with oxygen (generally derived from air) in the presence of a catalyst to produce a carboxylic acid product. In many cases the carboxylic acid will be a mixture of different carboxylic acids depending on the reactants, reaction conditions, etc. The carboxylic acids may be saturated or unsaturated. By way of example, acrolein and/or propylene may be oxidized to produce acrylic acid; and, isobutylene and/or t-butanol may be oxidized to produce a mixture of methacrylic acid and acetic acid as the main products.
In conducting such oxidation processes, the reactants are generally diluted with inert gas and/or steam for safety reasons and for better control of the heat of reaction. The reaction gas is thus generally very lean with respect to the carboxylic acid product and contains, in addition to the desired carboxylic acid product, varying amounts of unoxidized reactants, water vapor, carbon oxides, nitrogen, and various oxygenated hydrocarbon byproducts. The economics of these processes depend in a large part on how the carboxylic acid product is recovered, particularly on how the water is eliminated and separated from the reaction gas.
Various processes for recovery of the carboxylic acid products from gaseous mixtures including water as a component are disclosed in the prior art. For example, U.S. Pat. No. 3,932,500 issued Jan. 13, 1976 to Gerd Duembgen, et al. discloses the recovery of acrylic acid from gaseous mixtures obtained in the vapor phase oxidation of propylene and/or acrolein by scrubbing the gaseous mixture with a hydrophobic solvent (while avoiding the formation of an aqueous phase) so as to absorb the acrylic acid into the solvent. Specific solvents disclosed include hydrocarbons and diphenyl ether. Also, U.S. Pat. No. 3,868,417 issued Feb. 25, 1975 to Gerd Duembgen, et al. discloses recovery of acrylic acid from gaseous mixtures by absorption techniques utilizing esters of carboxylic acids. Even though these methods and other prior art methods may be used to advantage, they suffer various drawbacks. For example, the process disclosed in U.S. Pat. No. 3,932,500 does not effect separation of any acetic acid that may be present with the acrylic acid in the reaction gas. New and better processes are thus constantly being sought by the industry.
It is thus an object of the present invention to provide a process for separation and recovery of a substantially anhydrous carboxylic acid product from gaseous mixtures containing such carboxylic acids and water. It is an additional object of the present invention to provide a process for treatment of a reaction gas obtained from the vapor phase oxidation of hydrocarbons and/or oxygenated hydrocarbons and containing carboxylic acid product therein so as to recover a substantially anhydrous carboxylic acid product therefrom. Additional objects will become apparent from the following description of the present invention.